The present invention relates generally to thin film deposition and etching systems. In particular, the present invention relates to methods and apparatus for depositing thin films with very high uniformity or etching material at a highly uniform etch rate.
There are three common techniques used to deposit thin films onto substrates. These techniques are evaporation, magnetron sputtering, and ion beam deposition. FIG. 1 illustrates a schematic diagram of a prior art electron beam evaporation deposition system 10. The evaporation system 10 is enclosed in a vacuum chamber 12. An electron gun 14 generates an electron beam 16 that is used to heat a crucible 18 containing the deposition material to a temperature that causes the deposition material to evaporate. The electron beam is deflected with a magnet 20 that causes the electron beam to strike the desired location in the crucible 18. Typical evaporation systems have multiple crucibles.
Some evaporation systems include multiple electron guns that allow deposition material from two or more sources to be deposited simultaneously onto a substrate. Alternatively, a thermal heating element (not shown) is used to heat the crucible 18. A substrate support 22 that typically supports multiple substrates 23 is positioned in the path of the evaporated material. In order to increase the uniformity of the deposited thin film, the substrate support 22 may be rotated with a motor 24.
Magnetron sputter deposition systems use a diode device and a magnet to generate a plasma. A target is biased to a negative potential that is high enough to induce a breakdown in the surrounding gas and to sustain a plasma. The target atoms are sputtered onto the substrate to be deposited, which is placed in front of the target at a distance ranging typically between two and ten inches. The magnet is used to generate a magnetic field behind the target in order to trap the electron, thereby enhancing the bombarding efficiency of the ions.
FIG. 2 illustrates a schematic diagram of a prior art ion beam sputter deposition system 50. The ion beam sputter deposition system 50 is enclosed in a vacuum chamber 52. An ion source 54 generates an ion beam 56 that is directed to one or more targets 58. The ion beam 56 strikes the target 58 and sputters neutral atoms from the target 58 with a deposition flux 60. A substrate support 62 that typically supports multiple substrates 64 is positioned in the path of the deposition flux 60. The deposition flux 60 bombards the substrates thereby depositing a sputtered thin film. In order to increase the uniformity of the sputtered thin film, the substrate support 62 may be rotated with a motor 66. Ion beam sputtering is advantageous because it permits independent control over the energy and current density of the bombarding ions.
The thickness uniformity achieved with these prior art techniques is limited by the flux uniformity at the substrate plane and the type of substrate rotation. The flux uniformity can be adversely affected by target or deposition material imperfections that cause hot and cold spots. Typically, the flux uniformity changes with time. The flux uniformity can be improved somewhat by using a large target and by using a long distance from the target to the substrate. However, there are practical limits to the size of the target and the distance from the target to the substrate. Highly uniform thin films cannot practically be achieved with these prior art techniques.
The present invention relates to methods and apparatus for processing thin films with very high uniformity. A deposition system according to the present invention includes a beam aperture and/or a dual-scanning system that improves deposition uniformity. A method according to the present invention passes deposition flux from a deposition source though an aperture and translates substrates relative to the deposition flux with a first and a second motion. In one embodiment, the thin film uniformity is improved by scanning one motion much faster than the other motion. In another embodiment, thin film uniformity can be improved by over-scanning at least one type of motion.
Accordingly, the present invention features a deposition system. The deposition system includes a deposition source that generates deposition flux comprising neutral atoms and molecules. In one embodiment, the deposition source is an ion beam sputter deposition source that includes an ion source and a target that is positioned in the path of the ion beam. The target generates the deposition flux when exposed to the ion beam. In one embodiment, the ion beam sputter deposition source comprises a magnetron sputtering source. In one embodiment, the deposition system also includes an ion source that generates an ion beam that strikes the deposition area for ion beam assisted deposition.
A shield defining an aperture is positioned in the path of the deposition flux. The shield passes the deposition flux though the aperture and substantially blocks the deposition flux from propagating past the shield everywhere else. In one embodiment, the aperture is shaped to increase the transmitted deposition flux. In one embodiment, the aperture is shaped to reduce the over-scan area. A substrate support is positioned adjacent to the shield.
The deposition system also includes a dual-scanning system. By dual-scan we mean a scanning system that scans the substrate support relative to the aperture with a first and a second motion. The first and the second motion may be any type of motion such as translational or rotational motion. The first and the second type of motion may be the same or different types of motion. For example, in one embodiment, the dual-scanning system scans with a translational and a rotational motion. In another embodiment, the dual-scanning system scans with a first and a second translational motion.
In one embodiment, the scan rate of one motion is substantially greater than the scan rate of the other motion. For example the scan rate of one motion can be at least five times greater than the scan rate of the other type of motion. In one embodiment, the scan rate of at least one of the motions varies with time during deposition.
The dual-scanning system may be any type of scanning system that scans the substrate support relative to the aperture with two motions. In one embodiment, the dual-scanning system includes a rotational scanning system and a translational scanning system. The rotational scanning system causes a rotational motion having a rotational rate. The translational scanning system causes a translational motion having a translation rate. In one embodiment, the rotational motion is at least five times greater than the translation rate of the translational motion.
The deposition system may include a baffle that causes a pressure at the deposition source to be higher than the pressure at the substrate support. The deposition system may include a gas manifold that is positioned so as to cause a pressure at the deposition source to be higher than the pressure at the substrate support. The deposition system may also include an in-situ monitoring system that monitors properties of the thin film during deposition.
The present invention also features a method of depositing a uniform thin film. The method includes generating deposition flux. In one embodiment, the deposition flux is generated by ion beam sputtering. In another embodiment, the deposition flux is generated by evaporation. A substrate is scanned relative to the deposition flux with a first motion and a second motion, thereby depositing a uniform thin film onto the substrate.
The scan rate of the first motion is substantially greater than the scan rate of the second motion. In one embodiment, the first motion is a rotational motion having a rate of rotational and the second motion is a translational motion having a translational scan rate. For example, the rotational rate of the rotational motion may be five times greater than the translational scan rate in the translational dimension.
In one embodiment, the method includes passing the deposition flux through an aperture, thereby increasing the deposition flux. The method may include overscanning the substrate relative to the deposition flux with at least one of the first motion and the second motion. The method may also include monitoring deposition parameters of the thin film in-situ.
The present invention also features an ion beam sputter deposition system that includes an ion source that generates an ion beam. A target is positioned in the path of the ion beam. In one embodiment, the target is a compound target having at least two different target materials. In one embodiment, the target is rotatable with at least two target faces. When the ion beam strikes the target, neutral atoms and/or molecules are sputtered from the target with a deposition flux.
A shield defining an aperture is positioned in the path of the deposition flux. The shield passes the deposition flux though the aperture and substantially blocks the deposition flux from propagating past the shield everywhere else. In one embodiment, the aperture is shaped to increase the transmitted deposition flux. In one embodiment, the aperture is shaped to reduce the over-scan area. A substrate support is positioned adjacent to the shield.
The ion beam sputter deposition system also includes a rotational and a translational scanning system that scans the substrate support relative to the aperture. The rotational scanning system produces a rotational motion having a rotational rate. The translational scanning system produces a translational motion having a translation rate. In one embodiment, the rotation rate is substantially greater than the translational rate. For example, the rotation rate may be at least five times greater than the translation rate. The rotation rate and/or the translation rate may vary with time during deposition.
The ion beam sputter deposition system may include differential pumping. The ion beam sputter deposition system may include a vacuum pump having an inlet that is positioned relative to the target and the substrate support so that a pressure at the substrate support is lower than a pressure at the target. The deposition system may include a baffle that causes the pressure at the substrate support to be lower than the pressure at the target.